Abstract

Livestock manure, crop residues, woody materials, and compost made from these materials, are evaluated based on the characteristics of their decomposition in soil. This paper discusses the ability of organic material to affect the nitrogen supply over one cropping season, taking into account the C/N ratio and decomposition rate of the organic matter. Other factors discussed include the effect of organic materials to slow down the rate of nitrogen release and accumulate as organic matter in the soil. The efficient utilization of materials is also discussed.

Introduction

Soil fertility is one of the most important factors in crop production. Repeated applications of mature compost made from farmyard manure or rice straw is often recommended in Japan, in order to maintain soil fertility.

However, the use of composted organic materials has been gradually decreasing in Japan over the last few decades, because of the labor shortage and farm mechanization, and because most farms which produce crops no longer keep livestock.

At the same time, the direct application of crop residues has increased. Some of the manure produced on intensive livestock farms is used in a raw form, while some of it is mixed with a little bedding or straw. This is because livestock farms are producing more manure than can be applied to their own farmlands, and the excess has to be taken away to use on crop farms elsewhere.

Various kinds of compost made from livestock manure and diverse organic materials, such as sawdust, bark and so on, are being made for sale by commercial companies, and also by agricultural cooperatives and individual livestock farms. These diverse materials are being used because of a shortage of suitable raw materials such as straw.

The main objectives in applying organic matter are to supply balanced plant nutrition, to increase soil fertility (including the ability of soil to release nitrogen slowly), and to build up the level of soil organic matter.

The ability of organic materials to do these things is strongly influenced by the process of their decomposition process in the soil, as well as their nutrient content. However, the behavior of various organic materials in soils is not yet clear, because of the diversity of their components and varying levels of compost maturity.

This report attempts to evaluate various kinds of organic materials according to the pattern of their decomposition in soil.

Decomposition of Organic Materials in Soil

The decomposition of 11 kinds of organic material mixed with soil in a rice field in Japan is shown in
Fig. 1(50) (Maeda and Shiga 1978). The rate of decomposition was measured by the grass fiber-filter paper bag method (Maeda and Onikura 1977). The field was submerged from June 20 to the end of August.

The decomposition of excess sludge produced in the activated sludge process by a food processing plant and poultry manure was very fast. When the sludge was mixed with soil under upland conditions, almost half the carbon had been lost by the 40th day. The decomposition rates of rice straw, dried cattle manure and papermill sludge were slightly slower, as was that of immature rice straw compost. Compost made from papermill sludge, rice straw or sawdust mixed with swine manure decomposed slowly. Raw sawdust was the slowest to decompose.

Furthermore, the mineralization of nitrogen was rapid in excess sludge (C/N ratio: 6.3) and poultry manure (C/N:6.0). About 70% of total nitrogen had been mineralized 40 days after the sludge had been mixed with soil. This was followed by cattle manure (C/N:15.5), composted sawdust mixed with swine manure (C/N:22.0), mature rice straw compost (C/N:12.5) and composted papermill sludge (C/N:28.0). The rate of nitrogen mineralization was slow in moderately mature rice straw compost (C/N: 15.8) and slowest in immature rice straw compost (C/N:24.6).

In raw materials with a high C/N ratio, such as rice straw (C/N: 60.3), papermill sludge (C/N:140) and sawdust (C/N:242), the level of nitrogen in the grass fiber-filter paper bags increased. This was the result of immobilization of nitrogen which had diffused into the bags from the surrounding soil.

It should be noted that the rate of nitrogen mineralization is not always related to the C/N ratio of the organic materials.

A second study of the decomposition processes of 17 kinds of organic materials was carried out over five years, using the same methods in the same experimental field (Shiga
et al. 1985). The results of the second experiment are shown in
Fig. 2(54),
Fig. 3(49)
Fig. 4(39).

The rate of decrease in carbon in the organic materials was almost the same as that of nitrogen in materials with a C/N ratio of about 10 (
Fig. 2(54)). In materials with a high C/N ratio, the decrease in carbon was greater than that of nitrogen (Figs. 3
Fig. 4(39)).

The rate at which organic matter decomposed, as reflected in the decrease in carbon, differed markedly according to the origin or the formation process of these materials. The approximate decrease in carbon content after five years was 90% in the case of excess sludge, rice straw and wheat straw; 70% in the case of cattle manure, sawdust composted with swine manure, rice husk and papermill sludge; and 50% or less in the case of composted straw and some other composted materials.

A close correlation (r = -0.924) was found between the decomposition rate of organic matter and the lignin content (expressed as a percentage on an ignition loss basis) (
Fig. 5(55)).

The rate of nitrogen mineralization varied widely, from 75% in excess sludge to -116% in wheat straw at the end of the first year. After five years, the rate varied from 91.7% in excess sludge to -174% in sawdust.

The rates of N mineralization are not always correlated with C/N ratios of organic materials, because nitrogen mineralization is influenced, not only by the C/N ratio of the material, but also by the decomposition rate of the particular type of organic matter (
Fig. 6(50)).

Characteristics of Organic Materials Based on Their Decomposition Pattern in Soil

Damage to Crops from Rapid Decomposition

Organic materials containing large quantities of easily decomposable organic matter, such as animal wastes, excess sludge and some kind of crop residues, sometimes have a harmful effect on crops.
Fig. 7(51) shows that the production of CO
2 from livestock manure mixed with soil reached a maximum after 4 - 7 days, because of the rapid decomposition of easily decomposable organic matter (Matsuzaki 1977). CO
2 production is highest in poultry manure, followed by swine manure and cattle manure, in that order.

Heavy applications of these organic materials to cropland may cause a reduced condition in the soil, oxygen deficiency in the plant roots, and the production of harmful substances such as organic acids or phenolic compounds. It is necessary to consider the quantity of the organic materials, any improvement of their properties, and the time of application, if organic materials containing plenty of easily decomposed organic matter are to be used efficiently.

Nutrient Supplying Ability

In general, the efficiency of inorganic forms of nutrients in organic materials is much the same as those in chemical fertilizers. However, the efficiency of phosphorous contained in livestock manure or compost is about 60 - 70% compared to chemical fertilizer.

The effect of nitrogen on plant growth may be divided into readily available nitrogen and slow-release nitrogen.

Content of Readily Available Nitrogen

Readily available nitrogen contained in organic materials is mineralized in the soil when crops are at an early stage of growth, and plays a similar role to commercial organic fertilizer. The content of this type of nitrogen varies according to the type of organic material.

Examples of the rate of nitrogen mineralization in various organic materials in the soil during one cropping season, or in some cases in the course of one year, are shown in
Table 1(52).

The rate of N mineralization is about 60 - 70% in excess sludge, livestock manure and in crop residues with a low C/N ratio, and approaches the same rate as commercial organic fertilizer. Crop residues and woody materials with a high C/N ratio immobilize more than 60% of mineral nitrogen.

About 10-30% of nitrogen is mineralized in the various types of compost and in raw cattle manure. The rate of nitrogen mineralization is not completely correlated with the C/N ratio. For instance, as
Table 1(52) shows, the C/N ratios of rice brown bran, cattle manure, sugarbeet tops, composted straw, mature rice straw compost and composted cattle manure mixed with sawdust, are almost the same. However, the level of mineralized nitrogen in these materials over one cropping season ranges from 9 to 83%. The rate of N mineralization is also influenced by the various patterns of decomposition in different kinds of organic materials, as indicated in
Fig. 6(50). If organic materials are divided into groups, based on their decomposition rate during the first year, there is a good correlation between the rate of nitrogen mineralization and the C/N ratio in each group.

The decomposition rate of organic materials is related to their lignin content (see
Fig. 5(55)). Thus, we can get an approximate estimate of the content of readily available nitrogen in organic materials from the lignin content, expressed as a percentage on an ignition loss basis, and the C/N ratio (Shiga
et al. 1985).

Increase in Slow Release Nitrogen

Slow release of nitrogen to supply the correct amount throughout the cropping season is one of the desirable features of an arable soil.

If a certain amount of organic matter is applied to a soil each year, part of the nitrogen is mineralized, while another part of the nitrogen accumulates gradually in the soil. The total amount of mineralized nitrogen derived from applied organic materials and accumulated nitrogen increases gradually over time. The mineralized nitrogen derived from accumulated nitrogen is usually released slowly. The amount of nitrogen which accumulates, and the amount of nitrogen mineralized every year, can be estimated by using the decomposition rates of organic nitrogen for several consecutive years, as indicated in
Fig. 8(50) (Shiga
et al. 1985).

The annual increase in nitrogen mineralization after successive applications of various organic materials over several decades were calculated, using the results indicated in Figs. 2
Fig. 3(49)
Fig. 4(39) and a three-compartment exponential decay model proposed by Uchida (Inoko 1985). Changes in the annual amounts of nitrogen mineralized derived from successive applications of 1 mt (on a dry matter basis) of organic materials over 50 years are shown in
Fig. 9(50) (Shiga
et al. 1985).

After the initial two or three years, increases in the amount of nitrogen mineralized each year were relatively small with regard to materials which release a large amount of nitrogen in initial years, such as excess sludge, poultry manure and cattle manure. Composted materials which release a relatively small proportion of their nitrogen in initial years showed a long-term increase in the levels of mineralized nitrogen and slow-release nitrogen with successive applications. The increase was particularly marked in the case of mature compost made from either cattle manure or rice straw, since these materials contain a relatively large amount of organic nitrogen.

In the case of long-term applications of wheat straw, sawdust and papermill sludge, the annual level of mineralized nitrogen was small.

Ability of Organic Matter to Accumulate in Soil

The accumulation of organic matter derived from successive applications of 1 mt (on a dry matter basis) of organic materials was calculated, using the results in Figs. 2, 3 and 4, and the same model mentioned above. The process of accumulation over 50 years is shown in
Fig. 10(51) (Shiga
et al. 1985). The total amount of carbon and nitrogen accumulated in the plow layer in the experimental field after annual applications of rice straw compost over 60 years correlated closely with the values calculated by this method.

The ability of organic matter to accumulate in the soil is high in the case of composted materials, intermediate in woody materials, and relatively low in the case of crop residues, livestock manure and excess sludge.

Changes in the Characteristics of Organic Materials after Processing

The characteristics of organic materials regarding decomposition and nitrogen supplying ability are changed by processing.

Fig. 11(49) indicates that composting cattle manure for one or two weeks clearly reduces the amount of easily decomposable organic matter it contains (Matsuzaki 1977).

In crop residues with a high C/N ratio, composting decreases the C/N ratio and increases the nitrogen supplying ability after the residues are incorporated into the soil (
Fig. 12(52)), (Shiga
et al. 1985).

In the case of livestock manure, which has a relatively low C/N ratio, composting sometimes slows down the rate of nitrogen mineralization in soil in the initial years. In the first five years, nitrogen mineralization was less in a mature compost of cattle manure with a 9:5 C/N ratio than in raw cattle manure with a C/N ratio of 15:5. This was because the rate of decomposition of organic matter in the compost was very low (
Fig. 13(54)). However, mineralization of nitrogen in composted cattle manure may exceed that in raw manure in later years, as indicated in
Fig. 9(50), because of the high nitrogen content of the compost.

A decrease in the mineralization of nitrogen has been recognized in poultry manure after composting, as shown in
Fig. 14(53) (Ushio
et al. 1997). The nitrogen in poultry manure is easily mineralized during pretreatment and composting. Some of the ammonia produced is lost, so that the C/N ratio of composted materials may increase. The organic matter remaining in compost decomposes slowly. For this reason, the nitrogen-supplying ability of composted poultry manure is lower than that of fresh manure.

Integrated Evaluation of Organic Materials

The effects of applying diverse organic materials, in terms of rapid and slow nitrogen release, and the accumulation of organic matter in soil, are compared in
Table 2(56). The organic materials were applied in quantities based on their dry matter weight, at rates close to levels in actual practical use. Five mt/ha of crop residues such as rice straw or wheat straw correspond to the straw yield. When straw is composted, the amount of organic matter is usually reduced by half by decomposition. Therefore, 2.5 mt of compost corresponds to 5 mt of raw material, while 5 mt of compost is similar to the level used by many farmers.

The amount of readily mineralized nitrogen in excess sludge and livestock manure is similar to that in organic fertilizer. Only a relatively small amount of readily mineralized nitrogen is present in compost, even at the 5 mt level, and is negative in woody raw materials and straw.

The readily mineralized nitrogen contained in these organic materials is usually mineralized at a relatively early stage of crop growth, and has decomposed two or three years later. The nitrogen mineralized from organic matter accumulated in soils is released slowly. The level of slowly mineralized nitrogen which mineralizes in the course of a year, 50 years after the application of organic matter began, is shown in
Table 2(56). The number is calculated by subtracting the nitrogen mineralized each year from the third year after application, from the nitrogen mineralized in the 50th year.

Long-term, repeated applications of cattle manure and various kinds of compost slowly increases the level of mineralized nitrogen, although the pattern of increase is different for each material (
Fig. 9(50)). This practice is an effective way of increasing soil fertility.

The accumulation of soil organic matter is limited with applications of excess sludge or poultry manure. The same may be true of swine manure, because of the small quantity applied and the rapid decomposition of the organic matter it contained. After repeated annual applications of 5 mt/ha of cattle manure and straw, 4 - 7 mt/ha of carbon accumulate in the soil, corresponding to about 0.4 - 0.7% of the total carbon in the plow layer at a depth of 10 cm.

The accumulation of organic matter is greater when 2.5 mt/ha of straw compost and mature cattle manure compost are applied, than when 5 mt/ha of these same materials are applied fresh without composting.

When raw materials are composted, more than twice the amount of organic matter accumulates than when the same amounts of raw materials are applied. Composting materials before they are applied may result in a clear improvement in the physical and chemical properties of the soil. Compost made of woody materials accumulates much more organic matter. Repeated applications of 5 mt/ha (on a dry matter basis) of composted material each year for 50 years causes about 1.5 - 2.7% of carbon to accumulate in the plow layer.

The ability of organic materials to supply nitrogen, increase soil fertility and cause organic matter to accumulate in soils, differs according to their origin and processing. Each material should be utilized and processed on the basis of its characteristics, and the objective of its utilization.

References

Inoko, A. 1985.
Mathematical Representation of Decomposition or Accumulation of Organic Matter in Soils. Research Report of Secretariat of Agriculture, Forestry and Fisheries Research Council No. 166, 34-38. (In Japanese).

Hyogo Agricultural Technology Center. 1989. Establishment of Technique of Vegetable Production in Rice Soil by Using Complex of Organic Materials. Report on Development of Regional Important Techniques. pp1-111. (In Japanese).

Maeda, K. and Y. Onikura. 1977. A method to determine decomposition of applied organic matter under field conditions.
Journal of Science of Soil and Manure,
Japan 48: 567-568. (In Japanese).

Matsuzaki, T. 1977. Studies on the utilization of animal waste in agriculture.
Bull. Agricultural Research Institute of Kanagawa Prefecture 118: 1-38. (In Japanese with English summary).

Shiga, H., N. Ooyama, K. Maeda and M. Suzuki. 1985. An evaluation of different organic materials by their decomposition pattern in paddy soils.
Bulletin of the National Agriculture Research Center 5: 1-19. (In Japanese with English summary).

Shiga, H., N. Ooyama, M. Suzuki, K. Maeda and K. Suzuki. 1985. The effect of organic matter management in paddy fields on the accumulation of organic matter, or on the nitrogen sources in soils and growth of rice.
Bulletin of the National Agriculture Research Center 5:21-38. (In Japanese with English summary).

Figure 3 Decreases or Increases in C and N in Organic Materials with a C/N Ratio of 50 - 200, after They Have Been Mixed with Soil in a Rice Field for 5 Years (Shiga
Et Al. 1985)

Notes:s:start,e:endof5years

Figure 4 Decrease or Increase in C and N in Organic Materials with a C/N Ratio of More Than 200, after They Have Been Mixed with Soil in a Rice Field for Five Years (Shiga
Et Al. 1985)

Notes:s:start,e:endof5years

Figure 5 Relationship between Lignin Content and Decomposition or Organic Matter in Soil

Source:Shiga etal.1985

Figure 6 Relationship between Mineralization of Nitrogen and Initial C/N Ratio of Organic Materials. (Materials Are Grouped with Those with a Similar Decomposition Rate after 1 Year)

Source:Shiga etal.1985

Table 1 Rate of Nitrogen Mineralization in Diverse Organic Materials in Soil during One Cropping Season

Figure 7 Comparison of Co
2 Production from Different Livestock Wastes Mixed with Soil (30°C)

Source:Matsuzaki1977

Figure 8 Interrelation between the Decomposition of Applied Organic Matter, the Accumulation of Organic Matter by Successive Applications of Organic Matter, and the Yearly Decomposition of Organic Matter Derived from Both Organic Matter Applied in That Year and Accumulated Over Time (Schematic)

Note:Ratesarebasedontheamountoforganicmatterappliedinoneyear(=100%)

Figure 9 Changes in the Amount of Nitrogen Mineralized Each Year, Derived from Successive Applications of 1 MT (on a DRY Matter Basis) of Organic Materials for 50 Years